The objective of the currently funded project is to clarify the role of quantitative genetic factors in determining the levels of isoantibodies. With the permission of Dr. Landy, Chief, Extramural Programs, NIAID, the project was extended to include the levels of the immunoglobulins IgG, IgM and IgA. A renewal application was funded two years ago for further extending the project to include the causes and importance of variation in IgE and to clarify the basis of selective IgA deficiency. Although the studies have progresses well, the projected work on IgE will not be completed by the end of the present grant period (March, 1974). These studies have raised additional questions and the following are the objectives for this renewal proposal: a. To complete the quantitative genetic studies on IgE concentrations and to determine the degree of interrelation between IgE concentrations and the other immunoglobulins. b. To determine the differences in immunoglobulin levels between allergic children and non-allergic sibs in a new set of families containing one or more children suffering from allergies. c. To determine the causes of variation of salivary immunoglobulins. d. To evaluate quantitative genetic variation in immunoglobulins as a factor in the etiology of allergies. e. To develop the precipitin reaction of lectins against saliva into an efficient and reliable method for typing of secretor status.